I have a Browning BPS 12ga (28' barrel) that I use just for busting clays with my friends every now and then. Its a good gun for me since I'm left handed (bottom eject). What I'd like to know is what kind of recoil absorbing butt pad out there is best for this gun?
I've looked at Limbsaver and some others but the BPS is never listed on the chart on the back of the package. I've seen some slip-on ones but again I'm not sure which one fits. I don't want to change the LOP. Also, any idea how much a Gunsmith would likely charge to install a better pad? The slip-on ones look like they would make it harder to bring the gun up to shoulder.
Any ideas?

If you like the Limbsaver, then try to fit one to the gun. Take off the BPS recoil pad and take it to a shop with Limbsaver pads in stock. The package for LS is resealable so you can take out the pad and do a back to back comparison with the browning pad. I think a 1001 might fit your BPS, I may be wrong. Just try all the pads they have and see which one matches up to the Browning pad. If you don't find anything then you gotta get a fitted pad, those will run from 50 to 150 depends on the installer.

I see your in alameda. At the livermore range, everytime there is a state, or other major event.(check the website) There is a guy out there "trap guy, or trap dude" that does custom fits while you wait. Wanna say about 75 bucks complete. Have not used him personally, but I hear lots of great reviews from other members. There is also a guy in I beilive castro valley that I have heard good things about. Bill Martin certified gunsmith. # is 510-407-4602. Also as bj said, the kick ezz are nice.

Kick Eez pads are nice. I have two installed on my 1897 Winchester shotguns that I use for Cowboy Action Shooting. I do find them a little sticky and hang up on my clothes sometimes. Also they are a little fragile. I took a chunk out of one of mine already that I had to glue back in. Dont know how I did it. They do offer a coating to put on the to keep them from getting to sticky on your clothes. Midway sells them. Heres Kick Eez web site. >>> http://www.kickeezproducts.com/

I googled "Trap Dude" and found a strange site for a company in Fairfield that makes recoil pads but has very little else in the way of info on the site. I emailed them to see if they were the ones recomended by audiopro74 or not. Still waiting.
On the company sites for KickEez and Limbsaver they describe how to "grind and fit" their recoil pads for this gun. This makes me nervous to attempt since this gun has the closest thing to nice wood for a stock as I'm likely to ever have. I'd like to pay a pro to properly install. I'll try calling a few gunsmiths in the area for a price but am already cringing.

I just got off the phone with a place called Imbert & Smithers in San Carlos. They were very friendly on the phone and said they could install a new recoil pad on my BPS for around $100 or less. They had several brands available and would trim things to keep the LOP correct.
I've been in this place a few times in the past but have never bought anything. I remember them having lots of used shotguns and rifles there. I think I'll take this SG down there next week and give them a try.
I'll post how things went.

P.S. I also called Tabor's in San Bruno but they said that they didn't do that kind of work. But they were also very friendly and helpful on the phone.